The present invention relates to an electrical machine having two laminated rotor cores, which are arranged on a common shaft at a predetermined axial distance and each have axially extending cooling channels, and two laminated stator cores, which are associated with the laminated rotor cores. Furthermore, the present invention relates to an electrical machine having a housing, a laminated stator core and a laminated rotor core, which are arranged in the housing and of which at least one has axially extending cooling channels, and end winding areas at the end sides of the two laminated cores. In addition, the present invention relates to a corresponding method for cooling an electrical machine by passing an axial flow of a coolant through at least one cooling channel of a laminated rotor core and/or laminated stator core.
Electric motors, in particular asynchronous motors, are generally cooled by separate ventilation or self-ventilation. In the case of standardized, low-power motors, it is generally sufficient for there to be surface cooling. Low-power and medium-power traction machines require a higher level of cooling in the stator and rotor. For this purpose, axially extending cooling channels in the stator and rotor are provided with a coolant on one side. In the case of medium-power and high-power industrial machines, axial cooling channels are likewise provided in the rotor. The cooling channels are supplied with cooling air on one or both sides, and the cooling air emerges through radial cooling channels between two or more laminated core elements. In order not to allow the length of the laminated core to not become too great, the air gaps between the laminated core elements are only a few millimeters wide.
One problem when cooling with ambient air consists in the fact that the air can become contaminated with particles. However, in the case of a high content of dirt in the cooling air, narrow cooling slots would form relatively quickly and impair the cooling effect. In order to prevent this, a heat exchanger is usually provided in industrial machines. This ensures that only clean air circulates in the interior of the machine. In the case of traction machines, on the other hand, there is no installation space available for a heat exchanger owing to the narrow spatial conditions. In addition, this heat exchanger increases the temperature of the internal cooling air, which in turn limits the performance.
If the heat exchanger cannot be used, the cooling air needs to be filtered for the narrow cooling slots by means of a fine-pored air filter. In the case of a large deposit of dirt, this means changing the filter mat very frequently, which is undesirable and is not practicable, for example, in the case of dumper trucks in mining.
A generic electrical machine is known, for example, from the document U.S. Pat. No. 2,610,992. The laminated stator and rotor cores described therein have axially extending air cooling channels.
The German laid-open specification DE 44 13 389 also describes an electrical machine, which has two laminated rotor cores arranged on a common shaft at an axial distance from one another, two laminated stator cores arranged at a corresponding distance from one another and a cooling device, which has an air conveying device and cooling channels extending in the axial direction. Said cooling channels are each divided into two sections, as a result of the axial distance between the laminated cores, and are connected to the air conveying device such that a flow is passed through the two sections of each cooling channel in opposite directions. In the annular space between the laminated cores, the cooling air is deflected out of an axial direction into a radial direction, or vice versa. The axial distance between the laminated cores is in this case selected such that the flow cross section available for the cooling air in the annular space between the laminated cores is approximately equal to the sum of the flow cross sections of all of the cooling channels opening out directly into this annular space.